Effect of TKS159, a novel 5-hydroxytryptamine4 agonist, on gastric contractile activity in conscious dogs

A novel 5-hydroxytryptamine (5-HT)4 receptor agonist, TKS159, ¿4-amino-5-chloro-2-methoxy-N-[(2S,4S)-1-ethyl-2- hydroxymethyl-4-pyrrolidinyl] benzamide), has recently been developed as a gastroprokinetic drug. Cisapride is already used clinically to increase gastric contractions. The stimulatory effects of TKS159 and cisapride on gastric contractions were examined using force transducers chronically implanted on the vagally denervated pouch (Heidenhain pouch) and the vagally innervated main stomach in conscious dogs. Contractile activity was analysed by computer and expressed as a motor index. Intravenous administration of TKS159 or cisapride significantly increased the motor index in both the main stomach and the Heidenhain pouch during the fed and fasted states. Pharmacological characterization in the fasted state revealed that the contraction-stimulating activity of TKS159 and cisapride on the stomach was significantly inhibited by atropine, hexamethonium and a 5-HT4 receptor antagonist, SDZ 205-557. Granisetron (a 5-HT3 receptor antagonist) significantly inhibited cisapride-induced, but not TKS159-induced gastric contractions. The plasma motilin concentration was significantly increased after cisapride, but not after TKS159 injection. In conclusion, TKS159 has a contractile-stimulating effect on both the innervated and the denervated stomach. It is likely that a cholinergic pathway and 5-HT4 receptors are involved in producing the contractions, although other mechanisms cannot be excluded. Cisapride has almost the same characteristics, but the present findings suggest the involvement of motilin and 5-HT3 receptors in the effects of cisapride.